1. Field of the Invention
The present invention relates to a method of adjusting the brightness of a display device. More particularly, the present invention relates to a method of adjusting the brightness of a display device that utilizes brightness-adjusted feed-through voltages to deduce various level-adjust liquid crystal capacitance values so that optimized level-adjust voltages are obtained.
2. Description of the Related Art
The earliest types of dynamic images are documentary movies. Thereafter, with the invention of cathode ray tube (CRT), commercialized television broadcast has become so successful that almost every family has at least a television in their household. With the rapid development of the electronic technologies, CRTs have also been used as desktop monitors in computer systems so that CRTs were almost everywhere for several decades. However, due to the possibility of emitting hazardous radiation from various CRT-based display devices and the bulkiness of the display devices resulting from the electron gun design, CRT-based display devices can hardly be miniaturized, lightened up or scaled up to a larger size.
With the aforementioned problems for CRT, researchers has begun the development of the so-called flat panel display devices. Flat panel display device is a generic term for all display devices having a flat display surface, which includes the liquid crystal display (LCD), the field emission display (FED), the vacuum fluorescent display (VFD), the organic light emitting diode (OLED) and the plasma display panel (PDP). Due to the advantages of a large viewing angle, superior image quality and suitability for size scaling, PDP has a large market potential and is currently adopted in many types of digital televisions.
In the present-day technological level, using simulation software to modify level-adjust voltage in the process of developing new models saves development time as well as cost. In general, the major parameters required by the simulation are related to the pixel design. Aside from the liquid crystal capacitance (CLC), other parameters are fixed at the completion of the pixel design. Since the liquid crystal capacitance is related to the parameters of the liquid crystal, the effects due to material properties must be considered.
Different liquid crystals have different transparency rating versus display voltage (T-V) and liquid crystal capacitance versus display voltage (C-V) relations. A conventional twisted nematic (TN) liquid crystal pixel structure has a simpler structure design. Hence, a test cell can be fabricated and liquid crystal injected to measure the T-V and C-V relation of the liquid crystal. Thereafter, the capacitor equation:
  C  =            ɛ      0        ⁢          ɛ      r        ⁢          A      d      can be used to find the liquid crystal capacitance value of the pixel structure. Here, ε0 is the vacuum dielectric constant (a fixed value equals to 8.85e−14F/cm), εr is the liquid crystal dielectric coefficient (different liquid crystal has a different εr value), A is the area occupation of the liquid crystal capacitor and d is the separation between liquid crystal cells.
FIG. 8 is a flow diagram showing a conventional method of adjusting the brightness of a display device. In the conventional technique, the curve relating T-V and the curve relating C-V for the liquid crystal have already been measured in the process of fabricating the test cell. First, a computation of the gamma curve is carried out to obtain the transparency rating (T) of each level adjustment (S802). According to the transparency rating-display voltage (T-V) curve, the display voltage corresponding to the transparency rating for each level adjustment is obtained (S804). Thereafter, according to the liquid crystal capacitance value—display voltage curve, the liquid crystal capacitance value (CLC) corresponding to the display voltage for each level adjustment is obtained (S806). Finally, a simulation of the liquid crystal capacitance value of each level adjustment is carried out to obtain the best modulated ac driven positive, negative polarity optimized level-adjust voltage for each level adjustment (S808).
At present, the test cell structure of most TN liquid crystal display devices includes, from bottom to top, a glass layer, an indium-tin-oxide (ITO) layer, a LC layer, another indium-tin-oxide (ITO) layer and another glass layer. With the need for larger display panel and more television panels, the application of wide viewing angle technologies is definitely on the rise. However, unlike the simple TN type of display devices, the pixel design in wide viewing angle technologies is more sophisticated. For example, a display device having a multi-domain vertical alignment (MVA) design has bump or slit structures. In the design of such wide viewing angle display device, width, space and height all needs to be considered. In-plane switching mode (IPS) horizontal electric field are some of the major factors that needs to be considered. As a result, there are too many parameters and combinations to render the liquid crystal capacitance value obtained from testing a simple test cell valid.